1. Field of the Invention
The present invention relates to an apparatus for measuring a dispensing amount of liquid crystal drops and a method for manufacturing a liquid crystal display device by using the same.
2. Background of the Related Art
With rapid development of an information-oriented society, an urgent need has arose for an information display device having high-performance characteristics, such as good image quality, light weight, small thickness, and low power consumption. To meet this need, much research has been directed toward various flat panel display devices, such as Liquid Crystal Display Device (LCD), Plasma Display Panel (PDP), Electro Luminescent Display (ELD), Vacuum Fluorescent Display (VFD), and so on. Some of these display technologies have already been employed in various apparatuses as the information display device.
Of these flat panel display types, LCDs are the most widely used since such displays meet the above-noted high-performance characteristics. In displays for mobile devices such as for notebook computers, LCD technology has replaced CRT (Cathode Ray Tube) technology. In addition, for desktop displays such as PC monitor and TV sets, LCD technology has been developed and may soon replace CRT technology.
The LCD is manufactured through an array process for forming bus lines or switching devices (in a case of an active matrix type) such as thin film transistor (TFT) on one substrate (TFT substrate), color filter (CF) process for forming color filter on another substrate (CF substrate), cell process for assembling both substrates into unit panels, and module process for assembling a driver IC or a back light.
A liquid crystal cell process is a process to assemble a TFT substrate and a CF substrate prepared by the array process and the color filter process, respectively. Generally an empty cell is formed with a fixed thin gap between the first substrate and the second substrate then, liquid crystal is filled through an opening around the gap, thereby forming a liquid crystal panel.
Before filling a liquid crystal into an empty cell, an assembling process step is carried out. In the assembling process, the TFT substrate having the TFT arrays formed thereon, and the color filter substrate having color filters formed thereon and opposite to the TFT substrate, are assembled into a panel (empty cell) using a sealing material. For filling a liquid crystal into the empty cell, a liquid crystal vacuum filling method is used. The liquid crystal and the empty cell are loaded in a vacuum chamber, a filling hole around the sealing material in the empty cell is dipped into the liquid crystal. Then, an inside of the vacuum chamber is restored to atmospheric pressure, thereby filling the liquid crystal into the empty cell.
FIG. 1 is a drawing for explaining the liquid crystal filling process step using the related art vacuum filling method applied thereto.
Referring to FIG. 1, a liquid crystal 25 is disposed in a container 30 placed in a chamber 20. The chamber 20 is maintained in a vacuum state to remove moisture and air dissolved in the liquid crystal 25 or contained inside the container 25.
Then, to fill the liquid crystal 25 through liquid crystal filling holes by a pressure difference between a pressure in the cells 40 and a pressure in the chamber 20, the liquid crystal filling holes in empty cells 40 are dipped into the container 30 and brought into contact with the liquid crystal 25. Then, the chamber 20 is brought from higher vacuum state to lower vacuum state and eventually to atmospheric pressure state by introducing nitrogen gas N2 into the chamber 20. Next, after finishing filling of the liquid crystal 25 into empty cells 40, the liquid crystal filling holes are sealed, and the filled liquid crystal cells are cleaned.
However, the liquid crystal filling method has poor productivity because the method requires a long time for liquid crystal filling when the liquid crystal 25 is filled into the empty cells 40. The method requires cutting of a large assembled panel into unit panels (that is, empty cells 40), dipping of a part of the unit cells 40 into the container 30, and bringing the liquid crystal filling holes into contact with the liquid crystal 25 under vacuum. Moreover, a large sized LCD is liable to have some defects due to imperfect filling of the liquid crystal 25 into the cells 40.
As a result, a liquid crystal dropping method has been developed, in which a fixed amount of the liquid crystal is dropped and dispensed into a main sealing area formed around the TFT substrate onto an inner surface of the TFT substrate, and then the TFT substrate and the CF substrate are assembled into a large liquid crystal panel in a vacuum chamber.
The liquid crystal cell process using the liquid crystal dropping method can be explained briefly as follows.
Referring to FIG. 2, after carrying out an orientation step (1S) in which an orientation material is coated on the TFT substrate and the CF substrate, and a mechanical rubbing is carried out on both substrates for orienting molecules of the liquid crystal material, the TFT substrate and the color filter substrate are cleaned (2S). The TFT substrate is provided with a plurality of gate lines running in one direction at fixed intervals, and a plurality of data lines running in the other direction perpendicular to the gate lines at fixed intervals, a plurality of thin film transistors and pixel electrodes in a matrix pixel region defined by the gate lines and the data lines. The CF substrate is provided with a black matrix layer for shielding a light leakage of parts except the pixel region, a color filter layer, and a common electrode.
Then, the cleaned CF substrate is loaded on a stage of a seal dispenser, and a sealing material is coated on a periphery of unit panel areas on the CF substrate (3S). The sealing material may be a photo-sensitive resin, or thermo-curing resin. Meanwhile, no liquid crystal filling hole is required.
At the same time, the cleaned TFT substrate is loaded onto a stage of a silver (Ag) dispenser, and a silver paste material is dropped onto a common voltage supply line on the TFT substrate in the form of a dot (5S). Then, the TFT substrate is transferred to an LC dispenser, and a liquid crystal material is dropped onto an active array region of each panel (6S).
The liquid crystal dropping process is then carried out as follows. After a liquid crystal material is contained into an LC syringe before the LC syringe is assembled and set, air dissolved in the liquid crystal material is removed under a vacuum state, and the liquid crystal syringe is assembled into and set into, and mounted on the liquid crystal dispenser. When the TFT substrate is loaded on a stage of the liquid crystal dispenser, the liquid crystal material is dropped thereon using the liquid crystal syringe (6S), by dispensing a fixed amount of the liquid crystal material onto the TFT substrate with defined pitches inside of a coating area of the sealing material (the pixel region).
After the TFT substrate and the CF substrate are loaded into a vacuum assembling chamber, the TFT substrate and the CF substrate are assembled into a liquid crystal panel such that the dropped liquid crystal is uniformly spread over unit panel areas formed in the liquid crystal panel (7S). Then, the sealing material is cured (7S). The assembled TFT substrate and color filter substrate, that is, a large liquid crystal panel, is cut into individual unit panels (8S). Each unit panel is ground and inspected (9S), thereby completing manufacturing of the LCD unit panel.
However, the related art method for manufacturing a liquid crystal display device having the liquid crystal dropping method applied thereto has the following problems.
In the liquid crystal dropping method, controlling a dispensing amount of the liquid crystal onto the substrate is very important. If the dispensing amount of the liquid crystal is insufficient, air holes may be formed. If the dispensing amount of the liquid crystal is excessive, non-uniform display may result.
The liquid crystal is dropped and dispensed from a syringe in the liquid crystal dispenser onto substrates. After the syringe containing the liquid crystal is assembled and set, and it is mounted on the liquid crystal dispenser, it is made sure if assembling and setting of the syringe is properly done by measuring a dispensing amount of the liquid crystal drops before the liquid crystal is dropped and dispensed onto the substrate. Thus, the dispensing amount can be ensured to be within a proper error range.
As explained above, the proper assembling and setting of the syringe can be made sure after the syringe is mounted on the LC dispenser. Therefore, if it is detected that the syringe is assembled and set incorrectly, there is much inconvenience and a delay of time, because the syringe must be taken out of the LC dispenser, re-assembled and mounted again on the LC dispenser again. This inconvenience and delay can result in decreased productivity of a manufacturing line.